Field of the Invention
This disclosure is related to the field of polymer interlayers for multiple layer glass panels and multiple layer glass panels having at least one polymer interlayer sheet. Specifically, this disclosure is related to the field of acoustic polymer interlayers comprising multiple thermoplastic polymer layers.
Description of Related Art
Multiple layer panels are generally panels comprised of two sheets of a substrate (such as, but not limited to, glass, polyester, polyacrylate, or polycarbonate) with one or more polymer interlayers sandwiched therebetween. The laminated multiple layer glass panels are commonly utilized in architectural window applications and in the windows of motor vehicles and airplanes. These applications are commonly referred to as laminated safety glass. Its main function is to absorb energy, such as that caused by a blow from an object, without allowing penetration through the opening or the dispersion of shards of glass, thus minimizing damage or injury to the objects or persons within an enclosed area. Safety glass also can be used to provide other beneficial effects, such as to attenuate acoustic noise, reduce UV and/or IR light transmission, and/or enhance the appearance and aesthetic appeal of window openings.
The thermoplastic polymer found in safety glass can consist of a single layer of a thermoplastic polymer, such as poly(vinyl acetal) or poly(vinyl butyral) (PVB), that has had one or more physical characteristics modified in order to reduce the sound transmission through the glass. Conventional attempts at such acoustic dampening have included using thermoplastic polymers with low glass transition temperatures. Other attempts have included multilayer interlayers using two or more (such as three) adjacent layers of thermoplastic polymer wherein the layers have dissimilar characteristics (see, for example U.S. Pat. Nos. 5,340,654, 5,190,826, and 7,510,771). These multilayer interlayers typically comprise a soft layer having a single poly(vinyl acetal) resin having low residual hydroxyl content and two stiffer outer layers having a poly(vinyl acetal) resin having a significantly higher residual hydroxyl content. The soft layer provides acoustic damping properties, while the stiff layers provide handling, processing and mechanical strength of the interlayer. The stiff outer layers generally contribute very little to the acoustic damping properties.
Previous attempts to produce multiple layer interlayers (comprising at least two adjacent polymer layers) that reduce sound transmission through a multiple layer glass panel have relied on various compositional permutations or differences between the two or more layers. Conventional multiple layer interlayers have a soft layer that has a single resin and exhibits a single glass transition temperature and a lower dispersity in composition. One prior art method teaches the use of acetals of differing carbon length (see, for example, U.S. Pat. No. 5,190,826). Another prior art method teaches the use of differing polymerization degrees (see, for example, Japanese Patent Application 3124441A or U.S. Patent Application 2003/0139520 A1). Another method of varying the layers is the use of a PVB resin having residual acetate levels of at least 5 mole % in one of two adjacent layer as a compositional difference (see, for example, Japanese Patent 3,377,848 and U.S. Pat. No. 5,340,654). Finally, other methods use poly(vinyl butyral) resins having different plasticizer concentrations (see, for example, U.S. Pat. No. 7,510,771). All of these interlayers provide sound insulation properties only within a narrow temperature range and have resin compositions having a narrow distribution and low dispersity in composition.
In these interlayers, the residual hydroxyl content in the soft layer poly(vinyl acetal) resin and the amount of the plasticizer have been optimized such that the interlayer provides optimal sound insulation properties at ambient application temperatures for multiple layer glass panels, such as windshields and windows installed on vehicles and buildings, but at temperatures above or below the ambient temperature, the sound insulation properties may deteriorate significantly. For example, if the multilayer interlayer composition has been optimized such that the multiple layer glass panel comprising the multilayer interlayer has a maximum sound insulation performance at 20° C. in its coincident frequency region (such as in the region around 5,000 Hz), changing the application temperature by about 10° C. (decreasing the temperature to 10° C. or increasing the temperature to 30° C.) decreases the sound insulation significantly, such as by several decibels or more. Further lowering or increasing the temperature reduces the sound insulation performance even more.
Further, multiple layer glass panels produced with conventional multilayer interlayers can have desirable sound insulation in one region of the world at ambient temperatures, but in other regions of the world where the ambient temperatures differ the sound insulation may be lower or performance may only be mediocre. Even in the same world region, as the seasons change throughout the year and temperatures increase or decrease significantly, the sound insulation ability of the glass panels also changes.
Accordingly, there is a need in the art for the development of a multilayer interlayer that has sound insulation performance over a broad temperature range instead of only at one temperature, such as ambient temperature. More specifically, there is a need in the art for the development of multilayer interlayers having at least one soft layer that provides sound insulation performance over a broad temperature range.